Vasodilation (involving widening of blood vessels) such as trauma leading to dysfunction of nerve activity on blood vessels and inhibition of the vasomotor center in the brain or drugs such as vasodilators typically used to treat hypertensive individuals.

Excessive sweating is not a cause of hypovolemia, because the body eliminates significantly more water than sodium.[8]

Clinical symptoms may not be present until 10–20% of total whole-blood volume is lost.

Hypovolemia can be recognized by tachycardia, diminished blood pressure,[9] and the absence of perfusion as assessed by skin signs (skin turning pale) and/or capillary refill on forehead, lips and nail beds. The patient may feel dizzy, faint, nauseated, or very thirsty. These signs are also characteristic of most types of shock.

Note that in children, compensation can result in an artificially high blood pressure despite hypovolemia. Children will typically compensate (maintain blood pressure despite loss of blood volume) for a longer period than adults, but will deteriorate rapidly and severely once they do begin to decompensate. This is another reason (aside from initial lower blood volume) that even the possibility of internal bleeding in children should almost always be treated aggressively.

Also look for obvious signs of external bleeding while remembering that people can bleed to death internally without any external blood loss. ("Blood on the floor, plus 4 more" = intrathoracic, intraperitoneal, retroperitoneal, pelvis/thigh)

Also consider possible mechanisms of injury that may have caused internal bleeding such as ruptured or bruised internal organs. If trained to do so and the situation permits, conduct a secondary survey and check the chest and abdomen for pain, deformity, guarding, discoloration or swelling. Bleeding into the abdominal cavity can cause the classical bruising patterns of Grey Turner's sign or Cullen's sign.

Usually referred to as "Class" of shock. Most sources state that there are 4 stages of hypovolemic shock,[10] however a number of other systems exist with as many as 6 stages.[11]

The 4 stages are sometimes known as the "Tennis" staging of hypovolemic shock as the stages of blood loss (under 15% of volume, 15-30% of volume, 30-40% of volume and above 40% of volume) mimic the scores in a game of tennis: 15, 15-30, 30-40 and 40.[12] It is basically the same as used in classifying bleeding by blood loss.

Minor hypovolemia from a known cause that has been completely controlled (such as a blood donation from a healthy patient who is not anemic) may be countered with initial rest for up to half an hour. Oral fluids that include moderate sugars and electrolytes are needed to replenish depleted sodium ions. Furthermore the advice for the donor is to eat good solid meals with proteins for the next few days. Typically, this would involve a fluid volume of less than one liter, although this is highly dependent on body weight. Larger people can tolerate slightly more blood loss than smaller people.

External bleeding should be controlled by direct pressure. If direct pressure fails, a tourniquet should be used in the case of severe hemorrhage that cannot be controlled by direct pressure. Tourniquet use in civilian first-aid, is now advocated as part of the C-ABC approach. Other techniques such as elevation and pressure points are not always effective but should still be attempted. As a rule of thumb, anywhere you can feel a pulse can be used as a pressure point to stop bleeding (with the obvious exception of the carotid pulses). If a first-aid provider recognizes internal bleeding the life-saving measure to take is to immediately call for emergency assistance.

Emergency oxygen should be immediately employed to increase the efficiency of the patient's remaining blood supply. This intervention can be life-saving. [14]

The use of intravenous fluids (IVs) may help compensate for lost fluid volume, but IV fluids cannot carry oxygen in the way that blood can, however blood substitutes are being developed which can. Infusion of colloid or crystalloid IV fluids will also dilute clotting factors within the blood, increasing the risk of bleeding. It is current best practice to allow permissive hypotension in patients suffering from hypovolemic shock[15] both to ensure clotting factors are not overly diluted but also to stop blood pressure being artificially raised to a point where it "blows off" clots that have formed.

If the hypovolemia was caused by medication, the administration of antidotes may be appropriate but should be carefully monitored to avoid shock or the emergence of other pre-existing conditions[citation needed].

Fluid replacement is beneficial in hypovolemia of stage 2, and is necessary in stage 3 and 4.[13]Blood transfusions coupled with surgical repair are the definitive treatment for hypovolemia caused by trauma[citation needed]. See also the discussion of shock and the importance of treating reversible shock while it can still be countered.

For a patient presenting with hypovolemic shock in hospital the following investigations would be carried out:

Historically a term desanguination (from Latin sanguis, blood) was in use, meaning a massive loss of blood. The term was widely used by the Hippocrates in traditional medicine practiced in the Greco-Roman civilization and in Europe during the Middle Ages. The word was possibly used to describe the lack of personality (by death or by weakness) that often occurred once a person suffered hemorrhage or massive blood loss.

In cases in which loss of blood volume is clearly attributable to bleeding (as opposed to, e.g., dehydration), most medical practitioners of today prefer the term exsanguination for its greater specificity and descriptiveness, with the effect that the latter term is now more common in the relevant context.[16]